1. Field of the Invention
The present invention relates to an image forming apparatus with a document handling device for feeding original documents to a predetermined position.
2. Related Background Art
Among image forming apparatus such as copying machines, the use of document handling devices for feeding original documents to a predetermined position such as an exposure position, has been increasing for the purpose of alleviating the cumbersome handling of the original documents by the operator.
However, in case of feeding an original document to a predetermined position, the positional accuracy of stopping the original documents is very important. If the stopped position deviates from a predetermined position, the electrostatic latent image of a recording medium will also be deviated, thus causing a displacement of the reproduced image on the recording sheet.
For this reason, in order to stop the original document at a predetermined position, there have been proposed, for example;
(a) to provide a retractable stopper at a predetermined position and to stop the document in abutting relation therewith (U.S. Pat. No. 4,268,870); and PA1 (b) to count the pulses from an encoder, mounted on a document feeding motor, from a predetermined preparatory position of the document, and to stop said motor upon counting a predetermined number of pulses (U.S. Pat. No. 4,667,951, U.S. Ser No. 016,867 filed on Feb. 20, 1987 and U.S. Ser. No. 049,970 filed on May 15, 1987).
However the above-mentioned method (a) is complex in structure and expensive. Also it is not suitable for high-speed operation, since very thin documents may be bent at the stopped position.
On the other hand, in the method (b), the braking of the feeding motor can be achieved by electrical connection of both ends of said motor and/or combination of a magnetic brake with said motor, but certain error in the stopping position is unavoidable due to variation in load, time-dependent change in performance, inertia etc. For reducing such influences, the feeding speed may be lowered before braking, but such solution inevitably decreases the exchanging speed of the documents.